Magnetic techniques for evaluating peripheral nerve function

Experimental and theoretical studies of the magnetic field of isolated, giant nerve axons are being extended to the study of nerve bundles. The theoretical models use effective anisotropic conductivities that depend on the spatial and temporal frequencies of the transmembrane action potential to account for the effect of adjacent myelinated fibers on both the action current and the extracellular potential of a single axon off-axis in a sheathed nerve bundle. A convolution model is used to recreate the compound action signal from the fiber diameter histogram. A nonnegative least-squares algorithm is used for the deconvolution to obtain the histogram from measured signals, demonstrating the feasibility of magnetic determination of fiber diameter histograms. An openable toroidal probe is being developed to allow intraoperative assessment of damaged peripheral nerves in humans